Truxton, released in Japan as Tatsujin (タツジン), is a 1988 vertically scrolling, shoot 'em up arcade game developed by Toaplan, later ported to the Mega Drive (worldwide) and the PC Engine (Japan-only). Like many other scrolling shooters, the game is set in outer space, where the player takes control of a small spaceship across several planets. The game is played with an eight-way joystick and two buttons (a shot and a bomb button) through five large levels and their bosses (which then loop forever, at higher difficulties).

Story

Taking place somewhere in space: an armada of Gidans, led by the evil Dogurava, is invading the planet Borogo aboard five gargantuan asteroids. After surviving an attack on an orbiting Borogo cargo barge, a pilot enters one remaining fighter and challenges the Gidans in a desperate attempt to quell the alien invasion and divert their asteroid fortresses in the process.
Gameplay

The player's ship starts with a basic weapon, the Power Shot. By picking up various icons, the player can upgrade his/her ship:

S increases the ship's maneuvering speed, up to four times; any further icon is worth 5000 points.
B increases the number of "Tatsujin Bombs"/"Destroyer Bombs" available, and used with the bomb button; every life starts with 3. These are typical "smart bomb" devices which are dropped near the ship and destroy anything in their range. The Mega Drive port changes the effect to completely cover the screen (damaging anything in it), instead of the smaller portion from other versions.
Five Ps will increase the weapon level of the ship by 1 (maximum 3). Icons can be collected beyond that point, up to 10. These icons carry over between lives; after losing a life, if 5 to 10 icons are stored, the appropriate amount would be spent to give you weapon level 2 or 3. This system is fairly similar to Toaplan's later work, Fire Shark.
1UP or 2UP icons increase the number of lives. These are typically uncovered by shooting at a particular object with a certain weapon.

Weapon icons

Weapon icons are distinguished by their lack of a letter, and instead come in red, green, or blue.

Red represents the "Power Shot"; small red projectiles in a forward pattern with some spread. Balanced for just about everything, this is also the ship's starting weapon. In the arcade version, weapon level 3 is simply a wider spread; in the Mega Drive port, the shot of level 2 is retained, while the options create a "shield" of sorts instead.
Green represents the "Tatsujin Beam"/"Truxton Beam"; powerful, fast-moving green lasers, and the strongest weapon per projectile. Good for concentrated fire on larger and boss enemies, but has very little spread.
Blue represents the "Thunder Laser"; not a projectile, but ever-present lasers made of blue lightning that spread in all directions, with lock-on properties for larger enemies. Excellent spread and constant damage, but that damage is less than the Power Shot in most cases.

If you already have a particular weapon when you pick up that weapon's icon, the icon is worth 5000 points.

Description from Wikipedia.